The only reason Israel has been able to survive in the Middle East, and even to flourish there, is because its enemies’ armies are incompetent. When asked how and why Israelis win every battle, the celebrated general Moshe Dayan said it’s because they fight Arabs. “We’re a feuding people, not a warring people,” Lebanese historian Kamal Salibi said to me once in Beirut. “We haven’t been good at war for hundreds of years.” If Arabs could fight as effectively as, say, the Russians, Israel would have ceased to exist long ago.

Most likely it would have died before its first birthday. Syrian and Egyptian armies tried three times to destroy the Jewish state, and the Jordanian army tried twice. Hamas and the Palestine Liberation Organization have spent decades harassing Israel with terrorist, guerrilla, and low-level rocket attacks, but they’ve never come close to threatening the country’s existence.

Hezbollah—Lebanon’s Syrian- and Iranian-sponsored Party of God—is different. Hezbollah is the most formidable non-state army in the world and by far the deadliest and most effective fighting force ever fielded against Israel. And it’s just as sworn to Israel’s destruction as the would-be conquerors of the past. Nicholas Blanford’s gripping new book, Warriors of God, explains in peerless detail how Hezbollah grew into such a major force.

It began as a shadowy, ragtag terrorist-guerrilla group during the crucible of Lebanon’s civil war. After Israel’s withdrawal from South Lebanon in 2000, Hezbollah transformed itself into a wholly original hybrid of guerrilla army and conventional army. The Party of God’s partisans didn’t even have their own name in the early years. They made themselves famous with hostage-taking and airplane hijackings, but their most potent innovation—which transformed the face of the region—was the suicide bomber.

In November 1982, Imad Mughniyah, who would later become Hezbollah’s most skilled and hunted commander, told Fatah member Bilal Sharara he had found someone willing to blow himself up. “I laughed and thought he was crazy,” Sharara told Blanford. “Who would want to blow themselves up? No one had done anything like that at the time.” Suicide bombers are dangerous, but they’re weapons of the weak: it would be 18 years before the last Israeli soldier evacuated the “security zone” in South Lebanon. As the anti-Israel insurgency ground on, though, Hezbollah tacticians and fighters acquired better weapons and the skills to use them.

The Party of God hasn’t yet outworn its designation as a terrorist group—the United Nations accuses it of killing Lebanon’s former prime minister, Rafik Hariri, for instance—but it rarely resorts anymore to al Qaida-style attacks. Hezbollah now has an enormous rocket arsenal with the power not only to kill civilians in Israel, but also to sink Israeli ships and to blow up supposedly indestructible Merkava tanks with swarms of missiles.

During the 2006 war, Hezbollah fought Israeli ground troops with a highly sophisticated mixture of guerrilla and conventional tactics. “The resistance,” Secretary General Hassan Nasrallah boasted, “did not wage a guerrilla war. . . I want to clarify this point; it was not a regular army, but [it] was not a guerrilla [army] in the traditional sense, either. It was something in between.” Blanford quotes an Army War College study bolstering the Hezbollah chief’s claim. “Hezbollah’s position on the guerrilla-conventional continuum in 2006,” it said, “was much closer to the conventional end of the scale than non-state actors are normally expected to be.”

Today, Hezbollah’s rocket and missile arsenal is larger than that of most national armies. Not only does it stock thousands of relatively weak Katyusha rockets in bunkers, houses, and hillside launch sites; it also has ballistic missiles that can blow skyscrapers off the map in Tel Aviv. Its conventional strength means that it can now wreak far more havoc than a mere terrorist organization, but its well-honed guerrilla tactics make it just as hard to defeat.

Hezbollah scored its great victory in forcing the withdrawal of exhausted Israelis from their “security zone” in South Lebanon. It was the first time, arguably, that the Jewish state lost a war. Hezbollah, though, was never solely interested in the liberation of land. Its war of “unrelenting hostility,” as Blanford puts it, was always about the destruction of Israel. “The ‘resistance,’” he writes, “is Hezbollah’s beating heart, its one immutable defining certainty.” The Party of God said so explicitly in its first manifesto, the Open Letter of 1985, and Nasrallah has repeated that promise ever since he became the militia’s leader. “The elimination of Israel from existence,” he said in February of 2008, “is inevitable because this is a historical and divine law from which there is no escape.”

Hezbollah’s cult of death, nurtured during its suicide-bomber phase, is stronger than ever. Wherever Hezbollah has a serious presence in Lebanon, portraits of young “martyrs” hang from electrical pylons. The eliminationist rhetoric and dreams of total destruction are taken to heart by those willing to die to kill Israelis and Jews. “You cannot understand the joy of jihad unless you are in Hezbollah,” one of its fighters tells Blanford. Nasrallah himself refused to accept condolences when his own son was “martyred.”

Blanford refrains from condemning Hezbollah outright—partly, no doubt, because he wants to retain his nearly unparalleled access to its spokesmen, but also because it isn’t necessary. Readers seeking denunciations of terrorism and “resistance” will have to look elsewhere. The Party of God’s own actions and words suffice well enough to condemn it. If calls to destroy a sovereign U.N. member state don’t bother you, there isn’t much Blanford or anyone else can say that will change your mind.

While Blanford’s focus is Hezbollah, the portrait he paints of the Israeli occupation isn’t flattering, either. Israelis of nearly all political persuasions view Lebanon as their Vietnam, so to speak, since one disaster and botched operation after another led to an all-but inevitable defeat and withdrawal. Blanford, though, does a better job here than most of his Beirut-based colleagues. He’s seemingly aware, without actually saying so, that Israel is the subject of hysterical lies every day in the Arab world, and he almost always takes great care before accusing Israel of any wrongdoing.

Hezbollah’s war against Israel is now in its 31st year. None of the outstanding issues that led to conflict in the past (Israel’s existence being the primary one) have been resolved. And the “resistance” is stronger than ever. The rocket war in 2006 killed more than 100 Israelis, more than 1,000 Lebanese, five U.N. peacekeepers, and even a handful of Iranian Revolutionary Guards. It caused billions in damage and produced hundreds of thousands of refugees in each country. It convinced both sides that the next round will be the deadliest ever and to prepare accordingly. Israel won’t make the same mistakes, and it can’t afford to; next time, not only Tel Aviv and Jerusalem, but also Israel’s Dimona nuclear power plant, will be within Hezbollah’s missile range.

Hezbollah fighters hope the next war will be fought more in Israel than in Lebanon. “The resistance leadership might ask you to lead the resistance to liberate Galilee [in Northern Israel],” Nasrallah said to his cadres early last year. “God willing, we will go into Palestine next,” one fighter told Blanford. “Next time maybe the U.N. will ask us to withdraw from Northern Israel,” another said, “rather than Israel withdraw from South Lebanon.”

Ten years ago, Blanford wrote in Beirut’s Daily Starthat Hezbollah may be planning to storm Israeli border towns and seize hostages. “The revelation raised some eyebrows at the time,” he wrote, “but not anymore.” Hezbollah fighters aren’t (yet) sufficiently skilled or well-equipped to invade Israel and survive long enough to be asked to withdraw—but at the end of the day, they don’t have to. They have enough powerful missiles to inflict considerable pain without going anywhere. All they need to do is hide the launchers from Israeli aircraft—which they proved they can do during the last war—and use their guerrilla tactics to prevent Israeli soldiers from coming in and sabotaging the launch sites by hand.

Even with its bristling arsenal, Hezbollah still isn’t strong enough to destroy Israel. It probably never will be. But if its model of “resistance” is exported to enough of Israel’s neighbors—even if Iran fails to acquire nuclear weapons—the Jewish state may finally face the existential threat it has long feared. It may not be a likely scenario, but it has become an imaginable one.

Michael J. Totten is a contributing editor at City Journal. His first book, The Road to Fatima Gate, recently won the Washington Institute’s Silver Book Prize.